1. Field of the Invention
The present invention relates to a light measuring device, and more particularly, to a light-measuring device for a plane light source.
2. Description of the Prior Art
Measuring the brightness value or color temperature of a normal plane light source, such as a back-lit board or faceplate of a liquid crystal display (LCD), or a back-lit board of a scanner, is necessary to ensure the quality of the plane light source and to form a basis for adjusting the illumination characteristics of the plane light source.
One method of the prior art for measuring a plane light source is to measure a plurality of test points on the luminous surface of the plane light source with a photometer. A tester uses a photometer to detect the brightness value of each test point and then compute the average brightness value. However, for each test point to be tested, the tester must move the photometer to a predetermined position. Thus, the more test points there are, the more time is spent testing, and the more inconvenient the method becomes.
Another method of the prior art to effect the measurement is to use a digital camera to detect the brightness values or gray-level values of all areas on the luminous surface of the plane light source. From this the average brightness value or the average gray-level value can be computed. Although, with this method, the speed of the measurement is faster, the accuracy is not so high. The brightness values of the areas near the edge of the luminous surface register less than other areas of the luminous surface, and the digital camera is unable to analyze light that radiates at small angles from the luminous surface.
It is therefore a primary objective of this invention to provide a light-measuring device for a plane light source. The light-measuring device is able to measure light radiating from a luminous surface of a plane light source both quickly and accurately.
The light-measuring device comprises a photosensor, a light shield, a control device and a driving device. The light shield has a plurality of apertures. The light from the luminous surface of the plane light source projects onto the photosensor through the plurality of apertures of the light shield to form a plurality of non-overlapping photosensing areas on the photosensor. Each photosensing area on the photosensor generates a corresponding signal. The control device analyzes the corresponding signals to check the light from each corresponding area on the luminous surface. With the light-measuring device, a tester can adjust the color temperature and brightness values of the plane light source.